The present invention relates to thin film electronic circuit components, and more particularly to providing low resistance, electrical contacts between dissimilar conductive films. It has been the practice to utilize thin films of aluminum as the primary conductive interconnect areas or bus bars between thin film transistors and associated thin film circuitry. It is possible to fabricate large area flat panel matrix display devices in which X-Y aluminum bus bars electrically interconnect thin film transistor circuit arrays which are disposed at individual display points defined between the intersecting bus bars. Aluminum is particularly effective as the bus bar conductor material because it is particularly easy to provide an aluminum oxide insulating layer between overlapping intersecting bus bars, which must be electrically isolated from each other. This well-insulated overlapping relationship of the aluminum bus bars is essential to eliminate any possibility of cross-talk between display elements and for a proper addressing sequence.
A particularly effective thin film transistor is disclosed in U.S. Pat. No. 4,040,073 owned by the assignee of the present invention, in which the source and drain contacts of the thin film transistor are fabricated of indium-copper. In fabricating a thin film transistor matrix array utilizing such thin film transistors with indium-copper source and drain contacts, literally thousands of connections must be made from such contacts to the X-Y aluminum bus bar films. It is also common practice to utilize an aluminum film as capacitor electrodes in such circuitry, and it is necessary to interconnect such capacitor electrodes to the indium-copper contacts of the transistors. A basic problem arises due to the incompatibility of aluminum and the indium-copper contacts. When aluminum overlaps the indium-copper, an unreliable joint or connection is produced during high temperature annealing of the thin film transistor, which is carried out at about 350.degree. C. A resistive junction or connection results due to diffusion and alloying of the indium with aluminum. This junction is characterized by structural irregularity and upon annealing at high temperature by failure of continuity.